fix accidental global
rename autoFocus to focusOnOpen; autofocus has native HTML meaning
Stateful: skip properties in HTML*Element.
getPropDescriptors() should check name of constructor, not prototype
Button: don't extend FormWidgetMixin and don't override native prop "type"
fix calling custom setters of watched props on FF
Fix Destroyable::own to return an actual array so that .forEach(...) can be used on the return value.
add jshintrc (but code is not reformated)